The azobenzene arsonate (ABA) group has been coupled to several target cells such as red blood cells and tumor cells. Killing of these targets has been achieved by antibody specific for the ABA group and complement, by antibody specific for the ABA group and normal guinea pig lymphocytes but not by ABA specific T cells. ABA target cells are apparently able to stimulate T cells and induce positive skin tests but not generate killer cells. Fatty acid conjugates of BSA produce lodalization patterns in lymph nodes of mice significantly different from BSA itself. This peculiar localization is accompanied by development of cell mediated immunity but no antibody. Its effect on tumor specific antigens will be sought.